1. Field of the Invention
This invention relates generally to breathing ventilators, and more particularly relates to a pneumatically driven, electronically controlled ventilator system for providing breathing gas to a patient, and a method and system for detection of disconnection and occlusion in an airway of the ventilator system.
2. Description of Related Art
A patient receiving breath pressure support from a ventilator system typically receives breathing gas through a patient circuit of the ventilator. The patient circuit generally consists of two flexible conduits connected to a fitting called a patient wye. The free ends of the conduits are attached to the ventilator so that one conduit receives breathing gas from the ventilator's pneumatic system, and the other conduit returns gas exhaled by the patient to the ventilator. The volume of the exhaled gas may then be measured in a spirometer before it finally exits through an exhalation valve. The wye fitting is typically connected to the patient's breathing attachment or enclosure, which conducts breathing gas into the lungs, and exhaled gas from the lungs to the exhalation branch of the patient circuit. The pneumatic system at the inspiratory end of the patient circuit is typically closed before a breath, and the exhalation valve at the exhalation end of the patient circuit is typically preceded by a one-way valve, to prevent gas from flowing retrograde in the exhalation branch of the patient circuit.
Occurrences of low pressures in the exhalation limb of the patient's breathing gas circuit during the exhalation phase of the pressure supported breath can be a cause of concern for the patient unless they are carefully controlled. Pressures in the patient lung that fall below PEEP (Positive End Expiratory Pressure, a baseline pressure value) can impair a patient's lung function, and it can be important to maintain PEEP in a patient's lung to prevent collapse of the lung.
Disconnections of a patient breathing circuit can occur at the inspiratory limb, the expiratory limb, the patient circuit wye, or between the endotracheal tube and the patient wye. Patient breathing circuit disconnections result in the patient receiving either no breathing gas or very little gas from the ventilator, and can interfere severely with maintenance of PEEP. During ventilation, it is also desirable to be able to assess the state of the tubing system so that conditions such as kinked tubes and high resistance filters that can occlude the flow of breathing gas and interfere with maintenance of PEEP are detected, to prevent injury to the patient attached to the ventilator, and so that increases in the work of breathing are minimized. It is also important to detect an occlusion condition in which the exhalation valve is stuck closed. Therefore, it is important to be able to detect disconnections and occlusions and to alert the respiratory therapist to these conditions. The present invention meets these needs.